With the rapid development of high-tech nowadays, it requires a substrate used in an electronic device with a high performance, high reliability and high density being made of a material with an excellent mechanical property, electrical property, thermal property and weldability. An essential assembly used in a power module is a direct bonded copper (short for DBC) substrate made of a metal-ceramic composite, which shows main features including high dielectric strength, current carrying capacity, and high thermal conductivity. Ceramics used in DBC substrate generally includes AlN, Al2O3 and BeO, which performance and thickness can be seen in following Table 1.
TABLE 1BendingThermalMaterialstrength/MPaconductivity/W/m · KThickness/mmAlN200-300140-270 (320 in theory)0.635Al2O3200-40020-300.38BeO—300—
It can be seen from Table 1 that, ceramic substrate made of AlN shows lower bending strength (200˜300 MPa), and the thickness may reach 0.635 mm when used in current IGBT power module. In addition, the production condition for ceramic substrate made of AlN is terribly harsh, together with high cost. Thus just a few companies, e.g. Maruwa and Kyocera, are capable of producing such ceramic substrate made of AlN. Otherwise, the thickness of the ceramic substrate made of Al2O3 may reach 0.38 mm, which greatly decreases the size thereof. But while using it in power module, the overall thermal resistance remains high, which causes the difficulty for heat radiation, and the fast speed of temperature rising. While using BeO for producing electronic packaging materials, the integrated performance is much better, but a poisonous property thereof limits its application.